Programming in Prolog: Using the ISO Standard

308 Pages·2003·4.509 MB·English

by  Prof. William F. Clocksin, Dr. Christopher S. Mellish (auth.)

Programming in Prolog
Springer-Verlag Berlin Heidelberg GmbH
W.F.Clocksin · C.S.Mellish
Programming
in Prolog
Fifth Edition
123
Prof.William F.Clocksin
OxfordBrookesUniversity
Department ofComputing
Wheatley Campus
Oxford OX33 1HX,United Kingdom
Dr.Christopher S.Mellish
University ofEdinburgh
Department ofArtificial Intelligence
80 South Bridge
Edinburgh EH1 1HN,United Kingdom
ISBN 978-3-540-00678-7 ISBN 978-3-642-55481-0 (eBook)
DOI 10.1007/978-3-642-55481-0
Cataloging-in-Publication Data applied for
Clocksin, W.F. (William F.), 1955-
Programming in Prolog: using the ISO standard/W.F. Clocksin, C.S. Mellish.--5th ed. p.cm.
Includes bibliographical references and index.
ISBN 978-3-540-00678-7 (alk.paper)
1.Prolog (Computer program language) I.Mellish, C.S. (Christopher S.), 1954-II. Title.
QA76.73.P76C57 2003
005.13´3--dc21 2003044177
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Preface to the Fifth Edition
SincethepreviouseditionofProgramminginProlog,theProloglanguagehas
been standardised by the InternationalOrganizationfor Standardization(ISO). Al-
thoughnotallPrologsystemsconformtothenewstandard,wefeltitwasnecessary
totaketheopportunitytoupdatethisbookinaccordancewiththestandard.Wehave
alsointroducedsomenewmaterial,clarifiedsomeexplanations,correctedanumber
ofminorerrors,andremovedappendicesaboutPrologsystemsthatarenowobsolete.
Thisbookcanserveseveralpurposes.Theaimofthisbookisnottoteachthe
artofprogrammingassuch.Wefeelthatprogrammingcannotbelearnedsimplyby
readingabookorbylisteningtoalecturer.You’vegottodoprogrammingtolearnit.
We hopethatbeginnerswithouta mathematicalbackgroundcan learnPrologfrom
thisbook,althoughinthiscasewewouldrecommendthatthebeginneristaughtby
a programmerwhoknowsProlog,aspartofacoursethatintroducesthestudentto
programmingassuch.Itisassumedthatbeginnerscanobtaintheuseofacomputer
that has a Prologsystem installed, and thatthey have been instructed in the use of
thecomputer.Experiencedprogrammersshouldnotrequireextraassistance,butwe
hopetheywillnotbedismayedatourintentiontorestrainmathematicalelaboration.
In our experience, novice programmersfind that Prolog programsseem to be
morecomprehensiblethanequivalentprogramsinconventionallanguages.However,
the same people tend not to appreciate the limitations that conventionallanguages
placeontheiruseofcomputingresources.Ontheotherhand,programmersexperi-
enced in conventionallanguagesare better preparedto deal with abstract concepts
such as variables and controlflow. But, in spite of this prior experience,they may
findPrologdifficultto adaptto,andtheymayneeda lotofconvincingbeforethey
considerPrologausefulprogrammingtool.Ofcourse,weknowofmanyhighlyex-
periencedprogrammerswhohavetakenupPrologwithmuchenthusiasm.However,
theaimofthisbookisnottoconvert,buttoteach.
Programming in Prolog can be a useful companion to two other books. The
beginner might use Programming in Prolog as a tutorial preliminary to the more
VI PrefacetotheFifthEdition
concise and advanced text Clause and Effect. The more experienced programmer
mightstartwithClauseandEffectandbewritingusefulprogramswithinafewhours,
returningtoProgramminginPrologtofillinanygapsinunderstanding.Clauseand
Effect also conforms to ISO Standard Prolog, and it may be beneficial to use the
reference manual Prolog: The Standard in conjunction with this book. Details of
thesebooksare:
ClauseandEffect,byW.F.Clocksin.
Springer-Verlag,1997.ISBN3-540-62971-8.
Prolog:TheStandard,byP.Deransart,A.Ed-Dbali,andL.Cervoni.
Springer-Verlag,1996.ISBN3-540-59304-7.
ProvidedthatthereaderisequippedwithaPrologimplementationthatconformsto
the ISO standard, the book Prolog: The Standard almost obviates the need for an
implementation-specific reference manual, although the latter would be useful for
documentingimplementation-definedparametersandlimits.
Like most other programminglanguages, Prolog exists in a numberof differ-
entimplementations,eachwithitsownsemanticandsyntacticpeculiarities.Inthis
book we have adopted a core Prolog based on ISO Standard Prolog. Previousedi-
tionsconformedtoadefactostandardthatbecameknownasEdinburghProlog.In
turn,EdinburghPrologwasthemaininfluenceonthespecificationofISOStandard
Prolog.Thetable shownbelowsummarisesthemainchangesthathavebeenmade
in the use of particularsyntactic forms, special atomsand built-in predicatessince
earlierversionsofthisbookinordertoconformtotheStandardorotherwisereflect
morerecentpractice.Mostofthe differencesbetweenthe EdinburghandISO core
versions are of a purely cosmetic nature, though ISO Standard Prolog has gone in
newdirectionsinthewaythatinput/outputishandled.
Thisbookwasdesignedtobereadsequentially,althoughitwillprovehelpful
toreadChap.8whenthereaderbeginstowritePrologprogramsconsistingofmore
thanabouttenclauses.Itshouldn’thurttobrowsethroughthebook,butdotakecare
nottoskipovertheearlierchapters.
Each chapter is divided into several sections, and we advise the reader to at-
tempt the exercises that are at the end of many sections. The solutions to some of
theexercisesappearattheendofthebook.Chapter1isatutorialintroductionthat
is intendedtogivethe readera feelforwhatis requiredto programin Prolog.The
fundamentalideasofPrologareintroduced,andthereaderisadvisedtostudythem
carefully. Chapter 2 presents a more complete discussion of points that are intro-
duced in Chapter 1. Chapter 3 deals with data structures and derives some small
exampleprograms.Chapter4treatsthesubjectofbacktrackingin moredetail,and
introducesthe cut symbol, which is used to controlbacktracking.Chapter 5 intro-
PrefacetotheFifthEdition VII
EdinburghEditions ISOEdition
"..."(string)notation Notused(canmeandifferentthings)
ASCIIcodesforcharacters Singleelementatomsascharacters
get,get0,put get_char,put_char
see,seeing,seen open,set_input,current_input
tell,telling,told open,set_output,current_output
user user_inputanduser_output
integer number(floating-pointnumbersarehandled)
reconsult consult(thoughnotintheStandard)
not \+
tab,skip notused
display write_canonical
assert asserta,assertz
/arithmeticoperator /and//operators
name atom_chars,number_chars
@<,@=<etc.introduced
=:=and=\=introduced
Table of differences between previous editions, which used theEdinburgh Prolog standard,
andthepresentedition,whichusestheISOstandard.
ducesthefacilitiesthatareavailableforinputandoutput.Chapter6describeseach
built-inpredicateinthestandardcoreofProlog.Chapter7isapotpourriofexample
programs collected from many sources, together with an explanation of how they
are written. Chapter 8 offerssome advice on debuggingProlog programs.Chapter
9introducestheGrammarRulesyntax,andexaminesthedesigndecisionsforsome
aspectsofanalysingnaturallanguagebyusingGrammarRules.Chapter10describes
therelationofPrologtoitsoriginsinmathematicaltheoremprovingandlogicpro-
gramming. Chapter 11 specifies a number of projects on which interested readers
maywishtopractisetheirprogrammingability.
During the past twenty years that previouseditions of this book have been in use,
individuals too numerous to list by name have given us help, support, encourage-
ment, suggestions, and comments about this book. We are grateful to our readers,
students,teachers,colleagues,correspondents,editors,friendsandfamilywhohave
contributedinvariousandmanifoldways.Ofcourse,responsibilityfortheerrorsand
omissionsthatremaininthiseditionrestsentirelywithus.
OxfordandEdinburgh WilliamClocksin
June2003 ChrisMellish
Table of Contents
1 TutorialIntroduction........................................... 1
GivesthestudentafeelforwhatitisliketoprograminProlog.
Introducesobjects,relationships,facts,rules,variables
1.1 Prolog.................................................... 1
1.2 ObjectsandRelationships ................................... 2
1.3 Programming.............................................. 3
1.4 Facts ..................................................... 4
1.5 Questions ................................................. 6
1.6 Variables.................................................. 8
1.7 Conjunctions .............................................. 10
1.8 Rules..................................................... 16
1.9 SummaryandExercises ..................................... 22
2 ACloserLook ................................................. 25
MoredetailedpresentationofPrologsyntaxanddatastructures
2.1 Syntax.................................................... 25
2.1.1 Constants........................................... 26
2.1.2 Variables ........................................... 27
2.1.3 Structures .......................................... 27
2.2 Characters ................................................ 29
2.3 Operators ................................................. 30
2.4 EqualityandUnification..................................... 32
2.5 Arithmetic ................................................ 34
2.6 SummaryofSatisfyingGoals ................................ 37
2.6.1 Successfulsatisfactionofaconjunctionofgoals .......... 38
X TableofContents
2.6.2 Considerationofgoalsinbacktracking .................. 42
2.6.3 Unification.......................................... 43
3 UsingDataStructures .......................................... 47
Representingobjectsandrelationshipsbyusingtreesandlists.
DevelopingseveralstandardPrologprogrammingtechniques
3.1 StructuresandTrees ........................................ 47
3.2 Lists ..................................................... 50
3.3 RecursiveSearch........................................... 53
3.4 Mapping.................................................. 57
3.5 RecursiveComparison ...................................... 60
3.6 JoiningStructuresTogether .................................. 63
3.7 Accumulators.............................................. 67
3.8 DifferenceStructures ....................................... 70
4 Backtrackingandthe“Cut”..................................... 73
Howasetofclausesgeneratesasetofsolutions.Using“cut”tomodify
thecontrolsequenceofrunningPrologprograms
4.1 GeneratingMultipleSolutions................................ 74
4.2 The“Cut”................................................. 80
4.3 CommonUsesoftheCut .................................... 85
4.3.1 ConfirmingtheChoiceofaRule ....................... 85
4.3.2 The“cut-fail”Combination............................ 90
4.3.3 Terminatinga“generateandtest”....................... 92
4.4 ProblemswiththeCut ...................................... 96
5 InputandOutput .............................................. 99
Facilitiesavailablefortheinputandoutputofcharactersandstructures.
Developingaprogramtoreadsentencesfromtheuserandrepresent
thestructureasalistofwords,whichcanbeusedwiththeGrammarRules
ofChapter9
5.1 ReadingandWritingTerms .................................. 100
5.1.1 ReadingTerms ...................................... 100
5.1.2 WritingTerms....................................... 101
5.2 ReadingandWritingCharacters .............................. 104
5.2.1 ReadingCharacters .................................. 105
5.2.2 WritingCharacters................................... 106